Ultra capacitors have a long way to go still.. They have leakage, and are limited by way of Vmax, unless you put them in series. Putting them in series creates a few problems; they are not very tolerant to overcharging, and when charging and discharging them (in series) those processes need to be very accurately balanced (easier said than done) under variable loads and states of charge. We won't be able to use them for practical purposes until we can get the Vmax up significantly without huge expense.

I'm working on a solution to this, but still need investors..